In the past, lightweight laminates have been utilized for complex-shaped structures such as aircraft and missile fuselage and wing panels. Traditionally, lightweight panels of this type have been formed from a plurality of stacked fabric sheets made from material such as fiberglass. Prior to the stacking of each sheet, it is covered with an appropriate resin material and the layers are built up one at a time. Then, great pressure is brought to bear upon the laminate, often requiring the use of an autoclave to and secure adequate bonding during curing.
More recent developments in the field have introduced foam layers in between fabric layers, as described in U.S. Pat. No. 4,034,137, issued July 5, 1977, to Hofer. In this patent, improved lightweight, high strength panels capable of flat or curved construction are constructed from laminated sheet structures comprising resilient open-celled organic resin foam impregnated with a thermosetting resin and compressed and bonded to surface layers of resin-impregnated fiber materials such as unidirectional graphite or fiberglass matted or woven cloth.
Although the disclosed method in the mentioned patent is an improvement over the earlier prior art, it necessitates the impregnation of each fabric layer of the laminate prior to the layer-by-layer buildup of the complete structure. This is quite time consuming and requiers special care to ensure satisfactory bonding between the foam layer and the sheets of fabric.